feat(0112): register kanban_cpp app in cpp/CMakeLists.txt + close issue

Adds add_subdirectory block for apps/kanban_cpp (lives in apps/ per issue
0096). The app itself is a sub-repo (gitignored via apps/*/), with its own
git history and master branch initialized.

Six panels reuse registry: http_request_cpp_core, kpi_card_cpp_viz,
sparkline_cpp_viz, agent_runs_timeline_cpp_viz, dod_evidence_panel_cpp_viz.
Backend Go on :8403 (independent operations.db from kanban_web).

dev/issues/completed/0112-kanban-cpp-app.md

@@ -1,7 +1,7 @@
 ---
 id: "0112"
 title: "App kanban_cpp: clon C++ ImGui de kanban_web con backend Go propio"
-status: pendiente
+status: completed
 type: app
 domain:
   - cpp-stack